Earlier, French media reported that an employee of NewEdge, which was created last month through the combination of the broking units of SocGen and French rival Calyon, had also been detained by French police.

Société Générale has confirmed that an employee working for its brokerage unit is being questioned by French police.

A spokesman for the group declined to give further details.

Dow Jones Newswires reports that earlier on Friday, justice officials said a share broker had been detained and was being questioned over links to rogue trader Kerviel.

Sources in London identified the broker as Moussa Bakir. SocGen would not confirm the name.

The broker, who works at the SocGen broking subsidiary, is suspected of having been aware of Kerviel's unauthorised trading, Le Monde newspaper reported on Friday.

Kerviel has been accused of incurring, through unauthorised trading, a €4.9bn ($7.1bn) loss at SocGen, France's second-largest bank.

SocGen is fully cooperating with the investigation, the bank's spokesman said.

Two days before the Société Générale losses were revealed on January 24, Fimat was merged with Calyon's broking subsidiary to create NewEdge.

When NewEdge was launched, its chief executive, Patrice Blanc, shrugged off turmoil in the world’s equity markets, arguing the new company’s credit rating and focus on derivatives would leave it well placed to service investors, particularly hedge funds.

“The creation of NewEdge could not have come at a better time. We operate in fast-moving industry where current economic uncertainties create plenty of opportunities for us.”

The news of a possible accomplice came just ahead of an appeal court hearing Friday afternoon in which a judge will rule whether to place Kerviel in detention.

Kerviel was freed under judicial supervision January 28 after he was charged with breach of trust and fabricating documents. However the state prosecutor has appealed against his release.